2
Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism

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CAFE July September 2008

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Rondenay et al., 2001; Bostock et al., 2002; Nicholson et al., 2004

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Episodic Tremor and Slip

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Array Analysis of Tremor McCausland

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CAFE Cascadia Arrays For Earthscope is all about water

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Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism

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Faults Never Die: They Just Get Reactivated!

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Local mantle hydration by pseudofaults Propagating Juan de Fuca ridge creates offsets in isochrones called pseudofaults Propagating Juan de Fuca ridge creates offsets in isochrones called pseudofaults Pseudofaults may hydrate the uppermost mantle producing 25% serpentine (McClymont and Clowes, 2005) Pseudofaults may hydrate the uppermost mantle producing 25% serpentine (McClymont and Clowes, 2005) Subsequent dehydration of this serpentine as it heats up during subduction appears to cause intraslab earthquakes in the mantle lithopshere Subsequent dehydration of this serpentine as it heats up during subduction appears to cause intraslab earthquakes in the mantle lithopshere Wilson, 2002 Washington Oregon British Columbia JDF ridge pseudofaults

19
Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism

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Intraslab Seismicity Largest intraslab earthquakes are in south sound region at base of microseismicity Largest intraslab earthquakes are in south sound region at base of microseismicity Deepest earthquakes are downstream from large events Deepest earthquakes are downstream from large events Intraslab seismicity is virtually absent north and south of arch Intraslab seismicity is virtually absent north and south of arch Mantle events coincide with subducted pseudofault Mantle events coincide with subducted pseudofault Intraslab focal mechanisms are widely scattered but generally are in-plane tension Intraslab focal mechanisms are widely scattered but generally are in-plane tension

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The largest intraslab earthquakes tend to occur at the base of the seismic zone.

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Local mantle hydration by pseudofaults Propagating Juan de Fuca ridge creates offsets in isochrones called pseudofaults Propagating Juan de Fuca ridge creates offsets in isochrones called pseudofaults Pseudofaults may hydrate the uppermost mantle producing 25% serpentine (McClymont and Clowes, 2005) Pseudofaults may hydrate the uppermost mantle producing 25% serpentine (McClymont and Clowes, 2005) Subsequent dehydration of this serpentine as it heats up during subduction appears to cause intraslab earthquakes in the mantle lithopshere Subsequent dehydration of this serpentine as it heats up during subduction appears to cause intraslab earthquakes in the mantle lithopshere Wilson, 2002 Washington Oregon British Columbia JDF ridge pseudofaults

27
Cascadia Intraslab Earthquakes Velocity at reflector varies from 7 to 8 km/s Velocity at reflector varies from 7 to 8 km/s West of 45-km Moho contour all events are at or below subducted Moho; wavespeeds are km/s West of 45-km Moho contour all events are at or below subducted Moho; wavespeeds are km/s East of 45-km contour, nearly all events are at or above reflector; wavespeeds are km/s East of 45-km contour, nearly all events are at or above reflector; wavespeeds are km/s

28
Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism

30
Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism

31
September, 2005 ETS (Thompson, Bennett and Johnson, 2006)

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(Melbourne, 2006)

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Kao et al., 2005

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Tremor spectra are similar to magnitude 1 earthquakes from 1-5 Hz Tremor are depleted in higher frequency energy

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Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism

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Dragert et al., Science, 2001

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Tremor events start in center and migrate NW and S

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Rogers et al., Science, 2003

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Primary Goal of CAFE Role of water in Cascadia subduction Role of water in Cascadia subduction How does water get into the subducting plate? How does water get into the subducting plate? Intraslab Earthquakes: Dehydration embrittlement Intraslab Earthquakes: Dehydration embrittlement Serpentine in mantle wedge Serpentine in mantle wedge Role of water in episodic tremor and slip Role of water in episodic tremor and slip Role of water in Cascade volcanism Role of water in Cascade volcanism